Ducted cooling arrangement for hydrostatic pumps

ABSTRACT

A hydrostatic pump assembly having an improved cooling arrangement. The pump assembly includes a hydrostatic pump having a housing which rotatably supports a drive shaft, and a fan is coupled to an external end of the drive shaft for rotation therewith. The housing includes a plurality of integrally formed, elongated fins which define a plurality of passages extending along the housing in a direction substantially parallel to the drive shaft. The housing also includes a flange at an end thereof proximate the cooling fan, the flange including at least one duct therethrough. The flange is secured to a wall of an implement with the housing disposed on one side of the wall and the cooling fan the opposite side of the wall. In operation, cooling air is drawn by the fan through the passages along the housing, and passes through the flange ducts at a relatively high velocity before being discharged radially from the fan on the side of the wall opposite the housing, thereby providing an enhanced cooling effect for efficient cooling of the pump.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydrostatic pumps of the type typically used with hydrostatic transmissions employed in the lawn and garden industry on self-propelled machines, such as riding lawn mowers, wide area walk-behind lawn mowers, and in other hydrostatic pump applications.

2. Description of the Related Art

Hydrostatic pump assemblies are well known in the art, and are commonly used for conversion of rotary motion into fluid motion. The pumped liquid, usually an incompressible liquid such as hydraulic oil, is normally received by and drives a motor which converts the fluid motion back into rotary motion. A typical example of a hydraulic system comprising such a pump and motor is a hydrostatic transmission for driving the drive wheel(s) of a riding lawn mower. The pump may be rotatably driven via a belt and pulley arrangement by the engine, and is in fluid communication with the motor via hydraulic fluid lines. The output shaft of the motor is coupled to the drive wheel(s). Typically, the speed at which the pump is driven is constant and the pump is of variable displacement, i.e., the quantity and direction of fluid moved thereby through the hydraulic system, and thus the speed and direction at which the motor is driven, are varied by changing the pump displacement.

A single pump driven by the engine may be used to drive a single motor, the motor being coupled to drive wheels through a solid axle or differential assembly. Alternatively, a pair of pumps driven by the engine may be individually in fluid communication with one of a pair of motors, each motor respectively coupled to a single drive wheel, as in a zero turn radius mower. Altering the displacements of the pumps individually controls the speed and direction of their respective motors and drive wheels.

As is well known, a pump's displacement control mechanism may include a pivotable swash plate internal to the pump housing and against which the pistons of the pump, which reciprocate in cylinders provided in a barrel driven by the pump's input shaft, bear. The angle of the swash plate can be variably controlled via a rotatable control shaft or trunnion arm engaged with the swash plate and to which the linkage is connected. The swash plate is variably angled to adjust the stroke of the pistons, and thus the displacement of the pump.

During operation of the hydrostatic pump, heat generated by the pump mechanism within the pump housing typically dissipates into the surrounding environment from the housing. The housing may be formed with integral fins to aid in dissipation of heat from the housing into the surrounding atmosphere. In some known hydrostatic pumps, a fan is mounted to an end of the drive shaft which extend externally of the housing to provide further cooling. During operation of the pump, the fan blows or draws cooling air over the housing. In some known pumps, an end cap of the housing includes a plurality of radially-extending fins which define a plurality of radially extending passages arranged around the drive shaft such that, upon rotation of the cooling fan, cooling air is blown or drawn through the passages to cool one end of the housing.

A disadvantage of the foregoing arrangement is that, because the cooling fins and passages are formed either in the end cap or otherwise only on one end of the housing, passage of cooling air therethrough cools only one end of the housing, and may not provide adequate cooling for the remainder of the housing.

Additionally, known fans typically discharge cooling air both radially and axially with respect to the direction of rotation of the fan and, depending upon the configuration of the implement with which the pump is used, the air circulated by the fan may not be able to readily escape the immediate vicinity of the housing, and may instead re-circulate around the housing, thereby decreasing cooling efficiency.

What is needed is a hydrostatic pump assembly having a cooling arrangement which is an improvement over the foregoing.

SUMMARY OF THE INVENTION

The present invention provides a hydrostatic pump assembly having an improved cooling arrangement. The pump assembly includes a hydrostatic pump having a housing which rotatably supports a drive shaft, and a fan is coupled to an external end of the drive shaft for rotation therewith. The housing includes a plurality of integrally formed, elongated fins which define a plurality of passages extending along the housing in a direction substantially parallel to the drive shaft. The housing also includes a flange at an end thereof proximate the cooling fan, the flange including at least one duct therethrough. The flange is secured to a wall of an implement with the housing disposed on one side of the wall and the cooling fan the opposite side of the wall. In operation, cooling air is drawn by the fan through the passages along the housing, and passes through the flange ducts at a relatively high velocity before being discharged radially from the fan on the side of the wall opposite the housing, thereby providing an enhanced cooling effect for efficient cooling of the pump.

In one form thereof, the present invention provides a hydrostatic pump assembly, including a housing; a drive shaft rotatably supported by the housing and including an end extending externally of the housing; a fan coupled to the drive shaft end for rotation therewith; and a plurality of fins formed integrally with the housing and extending along a substantial extent of the housing in a direction substantially parallel to the drive shaft, the fins defining a plurality of passages therebetween, whereby upon rotation of the fan, cooling air is drawn through the passages along the housing to cool the housing.

In another form thereof, the present invention provides a hydrostatic pump assembly, including a housing including a flange at one end thereof; a drive shaft rotatably supported by the housing, the drive shaft including an end extending externally of the housing; a fan coupled to the drive shaft end for rotation therewith, the fan disposed on a side of the flange opposite the housing; and at least one duct formed through the flange, whereby upon rotation of the fan, cooling air is drawn from around the housing, passes through the at least one duct, and is discharged from the fan.

In a further form thereof, the present invention provides a hydrostatic pump assembly, including a housing; a flange at one end of the housing, the flange including at least one duct therethrough; a drive shaft rotatably supported by the housing, the drive shaft including an end extending externally of the housing; a wall to which the flange is secured, the housing disposed on a first side of the wall and the drive shaft end extending through an opening in the wall to an opposite, second side of the wall, the opening aligned with the at least one duct; and a fan coupled to the drive shaft end for rotation therewith, the fan disposed on the second side of the wall, whereby upon rotation of the fan, cooling air is drawn from the first side of the wall around the housing to cool the housing, passes through the at least one duct and the wall opening, and is discharged from the fan on the second side of the wall.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a hydrostatic pump including an improved cooling arrangement according to the present invention;

FIG. 2 is another isometric view of the hydrostatic pump, showing the fan exploded away from the drive shaft;

FIG. 3 is a partial sectional view through the hydrostatic pump, taken along line 3-3 of FIG. 1; and

FIG. 4 is an isometric view of the hydrostatic pump, showing a wall in phantom lines to which the pump is attached.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention any manner.

DETAILED DESCRIPTION

Referring to FIGS. 1-4, a hydrostatic pump assembly 20 which includes an improved cooling arrangement according to the present invention is shown. Pump assembly 20 generally includes pump housing or casing 22 and end cap 24. As shown in FIG. 3, drive shaft 26 is rotatably supported within housing 22 by bearing 28 in housing 22 and an opposite bearing 30 in end cap 24. End cap 24 is attached to an open end of housing 22 via a plurality of fasteners 32, such as bolts. Drive shaft 26 includes end portion 34 extending externally of housing 22 beyond bearing 28, to which input drive pulley 36 and fan 38 are coupled for rotation with drive shaft 26, such as via a keyed or splined connection, for example.

Referring to FIG. 3, input drive pulley 36 is rotatably coupled via belt 40 to an engine (not shown) of an implement with which pump assembly 20 is used. The engine is typically driven at a fixed speed, and rotational motion from the output shaft of the engine drives drive shaft 26 of pump assembly 20 via belt 40 and pulley 36 to pump fluid from pump assembly 20 to a hydrostatic motor (not shown) to which pump assembly 20 is coupled via fluid lines (not shown). Pump assembly 20 includes a pump mechanism (not shown) therein which is driven by drive shaft 26. Further details of the pump mechanism, as well as the inlet and outlet structures of pump housing 22 to which fluid lines are attached, are disclosed in U.S. patent application Ser. No. 10/603,001 entitled HYDROSTATIC PUMP ASSEMBLY HAVING SYMMETRICAL END CAP, filed on Jun. 24, 2003, assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference.

As shown in FIG. 3, input drive pulley 36 and fan 38 are each separately coupled to drive shaft 26 and are spaced from one another, with fan 38 disposed closely proximate housing 22 and between housing 22 and pulley 36. Alternatively, input drive pulley 36 and fan 38 may be secured to one another, or may be integrally formed with one another from metal or from a suitable rigid plastic, for example.

Pump housing 22 includes a plurality of side walls 42, with one side wall including an opening 44 for receiving a swash plate angle control shaft or trunnion arm (not shown) which is rotatably manipulated through a linkage assembly (not shown) by an operator for altering the displacement of the pumping mechanism within housing 22. Additionally, side walls 42 of housing 22 may include one or more case drains (not shown) sealed with threaded plugs through which hydraulic fluid within housing 22 may be drained.

As shown in FIGS. 1-3, at least one side wall 42 of housing 22 includes a plurality of fins 46 integrally formed with housing 22, which extend longitudinally along a substantial portion of the long dimension of housing 22 and are oriented substantially parallel to the axis of drive shaft 26. Fins 46 define a plurality of passages 48 within the side walls 42 of housing 22 through which cooling air may be drawn by rotation of fan 38 to cool housing 22 in the manner described below. Housing 22 shown in FIGS. 1-4 includes fins 46 formed in two opposite side walls 42 thereof, however, fins 46 may also be formed in all four side walls 42 of housing 22 if desired. Any side walls 42 which do not include fins 46 of the type described above may optionally include other fins 47 disposed perpendicular to the long dimension of housing 22 to aid in dissipating heat from housing to the surrounding atmosphere.

Housing 22 additionally includes a mounting flange 50 integrally formed therewith at an end of housing opposite end cap 24. Alternatively, flange 50 may comprise a separate element from housing 22 attached to housing 22 in a suitable manner, such as by fasteners or by welding, for example. Flange 50 generally includes a pair of projections 52 extending from opposite sides thereof, with projections 52 including cutouts 54 through which fasteners may pass to secure housing 22 to an implement with which pump assembly 20 is used. For example, referring to FIG. 4, bolts 56 and nuts 58 are inserted through cutouts 54 and through openings in wall 60 of an implement or other structure with which pump assembly 20 is used to secure pump assembly 20 to wall 60. Wall 60 may be a portion of the frame of the implement, for example, and includes an opening 62 therein having an inner edge resting against annular shoulder 64 of flange 50, as shown in FIG. 3.

Referring to FIGS. 2 and 3, flange 50 additionally includes a plurality of passages or ducts 66 therethrough, shown in FIG. 2 as four ducts 66, which are formed generally between inner ring 68 and outer ring 70 of flange 50. Ducts 66 are aligned with passages 48 defined between fins 46, and are generally circumferentially disposed around drive shaft 26. Referring to FIGS. 2-4, fan 38 generally includes central hub 72 keyed or splined to end portion 34 of drive shaft 26, a generally flat plate portion 74, and a plurality of fins or vanes 76 extending from plate portion 74 toward housing 22, which are disposed closely adjacent flange 50 of housing 22.

Operation of the foregoing structures for cooling pump assembly 20 will now be described. During operation of pump assembly 20, drive shaft 26 is rotatably driven by the engine via belt 40 and input drive pulley 36 to in turn drive the pump mechanism within pump housing 22. The pump mechanism is selectively operable by an operator via a swash plate control, for example, to pump fluid at varying volumes from pump assembly 20 to the hydrostatic motor of the hydrostatic transmission via fluid lines and, during operation of pump assembly 20, heat is generated which must be dispersed from housing 22.

Rotation of drive shaft 26 also rotates fan 38 to induce a flow of cooling air from the surrounding atmosphere through passages 48 between fins 46, through ducts 66 in flange 50, and into fan 38 before being discharged from fan in the manner described below. More particularly, upon rotation of fan 38, a flow of cooling air is drawn through passages 48 between fins 46 longitudinally along side walls 42 of housing 22 to cool same, as designated by arrows A of FIG. 3. Advantageously, fins 46 provide an overall increase to the surface area of housing 22 which aids in the dissipation of heat therefrom, and cooling air passing through passages 48 closely adjacent fins 46 and side walls 42 of housing 22 facilitates the efficient transfer of heat from fins 46 and side walls 42 into the air flow. Also, the arrangement of fins 46 and cooling passages 48 described herein allows cooling air to be drawn by fan 38 along substantially the entire longitudinal extent of housing 22 in order to provide enhanced air flow around housing 22 to increase cooling efficiency.

Thereafter, as represented by arrows B in FIG. 3, the air passes through ducts 66 in flange 50 before being drawn into cooling fan 38. As the cross sectional area of ducts 66 is less than the volume around housing 22 and between fins 46, the velocity of the air flow increases as same passes through ducts 66. The air then passes into fan 38 substantially immediately after exiting ducts 66 due to the close proximity of fan 38 to flange 50. After entering fan 38 between vanes 76, the now warmed air is discharged from cooling fan 38 substantially evenly about fan in radial directions with respect to the rotational axis of fan 38, as indicated by arrows C in FIG. 3.

Advantageously, flange 50 and wall 60 provide a barrier or temperature gradient which defines a cooled region on a first side of flange 50 and wall 60 around housing 22 through which cooling air is drawn, and a warmed region on a second, opposite side of flange 50 and wall 60 in which the warmed air is discharged. In this manner, heat dissipated from housing 22 is captured within the cooling air flow and is then discharged by cooling fan 38 into the atmosphere on the second side of flange 50 and wall 60, which prevents re-circulation of the warmed air around housing 22 that would otherwise compromise the efficiency of cooling of pump assembly 20.

Although fan 38 operates as described above to draw air from around housing 22, through ducts 66, and then discharge air on the side of wall 60 on which fan 38 is disposed, rotation of fan 38 in an opposite direction would alternatively draw air into fan 38 from the side of wall 60 on which fan 38 is disposed, and push air through ducts 66 and around housing 22 to cool same. However, fore the reasons discussed above and as will be apparent to one of ordinary skill in the art, it is contemplated that this alternative operation would provide somewhat less efficient cooling of pump assembly 20 in most applications.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 

1. A hydrostatic pump assembly, comprising: a housing; a drive shaft rotatably supported by said housing and including an end extending externally of said housing; a fan coupled to said drive shaft end for rotation therewith; and a plurality of fins formed integrally with said housing and extending along a substantial extent of said housing in a direction substantially parallel to said drive shaft, said fins defining a plurality of passages therebetween, whereby upon rotation of said fan, cooling air is drawn through said passages along said housing to cool said housing.
 2. The pump assembly of claim 1, wherein said housing has a long dimension defined in a direction substantially parallel with said drive shaft, and said fins and said passages are elongate in profile and extend along said long dimension.
 3. The pump assembly of claim 1, wherein said housing includes a flange at and end thereof proximate said fan, said flange including at least one duct aligned with said passages, whereby cooling air is drawn through said at least one duct after passing through said passages.
 4. The pump assembly of claim 3, wherein said flange is disposed closely adjacent said fan, whereby cooling air is drawn into said fan substantially immediately after passing through said at least one duct.
 5. The pump assembly of claim 3, wherein said flange includes a plurality of said ducts, said ducts arranged circumferentially around said drive shaft and aligned with said passages.
 6. The pump assembly of claim 1, wherein said fan is shaped to discharge cooling air substantially radially evenly around said fan.
 7. The pump assembly of claim 1, in combination with a wall having a first side to which said housing is secured, said wall including an opening through which said drive shaft extends with said fan disposed on a second side of said wall opposite said first side, whereby cooling air is drawn from around said housing, through said wall opening, and is discharged on said second wall side.
 8. A hydrostatic pump assembly, comprising: a housing including a flange at one end thereof; a drive shaft rotatably supported by said housing, said drive shaft including an end extending externally of said housing; a fan coupled to said drive shaft end for rotation therewith, said fan disposed on a side of said flange opposite said housing; and at least one duct formed through said flange, whereby upon rotation of said fan, cooling air is drawn from around said housing, passes through said at least one duct, and is discharged from said fan.
 9. The pump assembly of claim 8, wherein said flange includes a plurality of said ducts spaced circumferentially around said drive shaft.
 10. The pump assembly of claim 8, wherein said flange is disposed closely adjacent said fan, whereby cooling air is drawn into said fan substantially immediately after passing through said at least one duct.
 11. The pump assembly of claim 8, wherein said fan is shaped to discharge cooling air substantially radially evenly around said fan.
 12. The pump assembly of claim 8, in combination with a wall having a first side to which said flange of said housing is secured, said wall including an opening aligned with said at least one duct and through which said drive shaft extends with said cooling fan disposed on a second side of said housing opposite said first side, whereby upon rotation of said fan, cooling air is drawn from around said housing, passes through said at least one duct, and is discharged from said fan on said second wall side.
 13. The pump assembly of claim 8, wherein said housing includes a plurality of elongated fins formed integrally with said housing and extending along said housing in a direction substantially parallel to said drive shaft, said fins defining a plurality of passages in said housing, whereby upon rotation of said fan, air is drawn through said passages along said housing to cool said housing.
 14. A hydrostatic pump assembly, comprising: a housing; a flange at one end of said housing, said flange including at least one duct therethrough; a drive shaft rotatably supported by said housing, said drive shaft including an end extending externally of said housing; a wall to which said flange is secured, said housing disposed on a first side of said wall and said drive shaft end extending through an opening in said wall to an opposite, second side of said wall, said opening aligned with said at least one duct; and a fan coupled to said drive shaft end for rotation therewith, said fan disposed on said second side of said wall, whereby upon rotation of said fan, cooling air is drawn from said first side of said wall around said housing to cool said housing, passes through said at least one duct and said wall opening, and is discharged from said fan on said second side of said wall.
 15. The pump assembly of claim 14, wherein said housing includes a plurality of elongated fins formed integrally with said housing and extending along said housing in a direction substantially parallel to said drive shaft, said fins defining a plurality of passages in said housing, whereby upon rotation of said fan, air is drawn through said passages along said housing to cool said housing.
 16. The pump assembly of claim 14, wherein said flange is disposed closely adjacent said cooling fan, whereby cooling air is drawn into said cooling fan substantially immediately after passing through said at least one duct.
 17. The pump assembly of claim 14, wherein said fan is shaped to discharge cooling air substantially radially evenly about said fan. 